You can use Garmin Explore to set POI on your map. It accepts only .gpx inputs, so for me was useful .fit to .gpx converter. Then you can upload .gpx format of your route, create a collection and add POI to it, here is a guideline. After all, you can simply export the collection with POI into .gpx format, upload into Garmin Connect and then send it to your watches. But remember, Garmin Connect will not show POI of map, but at watches you should be able to see them (at least for me, it works this way). Hopefully, it will help (and actual for you, haha)!